This invention relates to energy absorbing devices, movement dampers, and load limiters, and especially those that are all mechanical as opposed to hydraulic. Such devices are useful in many applications, dampers being particularly adapted to dampen recoil forces generated by firing a machine gun.
While hydraulic devices have often been used for damping recoil forces from guns or other apparatus, and such devices have certain advantages, they have the major disadvantage of requiring hydraulic fluid and the accompanying seals, which inevitably leak and require replacement. Systems that are all mechanical avoid these problems. Typically, such systems provide damping by virtue of the friction of sliding surfaces, and are sometimes referred to as Coulomb dampers. The damping provided is based on the coefficient of friction and is often thought of as basically a constant frictional force since the coefficient of friction is often referred to as a constant for a particular material. In fact, however, the coefficient of friction varies significantly during operation when subjected to variations in temperature, humidity, wear, foreign matter on the sliding surfaces, and other factors. In addition, the difference between static and dynamic friction is very significant. Consequently, a device relying on friction typically requires a much larger initial force or load to start movement than is required to continue movement.
There are many different types of mechanical dampers and energy absorbers, but nevertheless, a need still exists for improvements in such devices. It is particularly desirable that a recoil damper provide a substantially constant drag or damping effect from a standpoint of reliability and design of the system. That is, the requirements for a particular use may be accurately and efficiently met with a constant drag device. In addition, a constant drag device can function as an accurate load limiter which prevents movement of a structure until a predetermined load is applied. It is, of course, also desirable that such devices be compact, versatile and durable.